Ethylene and propylene are important basic chemical feedstock. Ethylene is used mainly in the production of polyethylene, ethylene oxide, ethylene glycol, polyvinyl chloride, styrene, vinyl acetate, etc. Propylene is used mainly in the production of polypropylene, cumene, carbonyl alcohol, acrylonitrile, propylene oxide, acrylic acid, isopropanol, etc. At present, ethylene and propylene are mainly produced through catalytic cracking or steam cracking of petroleum feeds. However, other processes for producing ethylene and propylene are paid more and more regard as the petroleum resource is being depleted and the prices of petroleum have been rising.
It has been known for some time that oxygenates, especially alcohols, are convertible into light olefins. There are numerous technologies available for producing oxygenates. For example, syngas may be produced from coal or natural gas and further converted into methanol. Therefore, producing light olefins from oxygenates, especially methanol, is a promising approach.
Chinese Patent Application CN1166478A discloses a method for producing light olefins such as ethylene, propylene, and the like from methanol or dimethyl ether, which method utilizes an aluminum phosphate molecular sieve as catalyst, and uses a circularly fluidizing process using an upward flow dense phase bed. Under preferred conditions including a reaction temperature of from 500 to 570° C., a space velocity of from 2 to 6 h−1, and a pressure of from 0.01 to 0.05 MPa, methanol or dimethyl ether is converted into light olefins, such as ethylene, propylene, and the like.
Chinese Patent Application CN1356299A discloses a process and a system for producing light olefins from methanol or dimethyl ether. This process utilizes a silicoaluminophosphate molecular sieve (SAPO-34) as catalyst, and uses a very shortly contacting fluidized bed reactor in which gas and solid co-flow downwardly. A feed contacts with the catalyst and reacts in the reactor, with the direction of the stream being downward; after exiting the reactor, the catalyst and reaction products enter gas-solid quickly separating unit located below the reactor to be quickly separated from each other; the separated catalyst is then passed into a regenerator to be regenerated by burning off carbon. This process achieves conversions of dimethyl ether or methanol of larger than 98%.
However, there is still need for a process for producing light olefins from methanol and/or dimethyl ether, which process achieves higher yield of and better selectivity to ethylene and propylene.